Human infertility is a global problem and failure of embryo implantation accounts for a significant percentage of pregnancy failure during both natural pregnancy and in vitro fertilization procedures. Implantation is an extremely complicated process requiring precisely controlled hormonal, growth factor signaling and cell-cell contacts which coordinate interactions between the competent blastocysts and the receptive uterus. In the past two decades we have greatly improved our knowledge on this subject by using sophisticated mouse genetics. However, our understanding of implantation is still rudimentary. Implantation research including the study of uterine receptivity and decidualization has benefited greatly from the Cre/LoxP technology which allows functional study of many genes in a tissue specific manner. Although inducible Cre/LoxP systems have been widely used in other fields of studies, their use in implantation studies has been limited by the steroidal nature of most of the inducers which interferes with the implantation process. The currently used Pgr-Cre and Amhr2-Cre lines are not inducible and each has their own limitations for implantation studies. Thus there is urgent need to develop an inducible tissue-specific Cre system for conditional deletion of genes in the uterus during implantation. In this proposal, we propose to knock rtTA into the endogenous Gli2 locus to generate a tetracycline-inducible line which in corporation with tetO-Cre can drive inducible Cre expression in the uterine stroma during implantation. In Aim I we will use BAC recombineering to generate a knock-in construct which will be used for gene targeting in ES cells and eventually germline chimera production. In Aim II, we will assess the usefulness of this knock-in allele in implantation studies. This mouse strain should be a valuable tool for researchers studying implantation as well as embryonic or postnatal organogenesis and carcinogenesis. PUBLIC HEALTH RELEVANCE: This project proposes to generate a tissue-specific inducible Cre system in the uterine stroma which can be used to knockout or overexpress gene of interest in the peri-implantation uterine stroma. This strain of mice will be an invaluable tool for reproductive biologists studying uterine receptivity, decidualization and placentation.